Design and performance investigation of a multi-pinhole collimator for a small field of view gamma imaging system

The aim of this study is to design a collimator for a gamma imaging system that has a small-footprint, a fast-scan-time, and a organ-specific applicability. To achieve such features, the collimator must have a high resolution, a high sensitivity, and a gantry with a simple geometry. For ensuring high resolution and high sensitivity, we designed a multi-pinhole collimator. For realizing a simplified gantry, we carried out studies with limited angle reconstruction. On the designed multipinhole collimator has eight-pinholes, whose diameters are 2 mm. Limited-angle reconstruction has been conducted with angle intervals of 3, 6, 9, and 12° and with an angle coverage of 60, 90, 120, 150, and 180°. The reconstruction of an image was separately developed based on the ray-driven and voxel-driven methods in order to overcome the sampling problem and to reduce the amount of computation required. To evaluate the performance of the designed system, performed studies on three spherical phantoms and a heart phantom by using the Geant4 application for tomographic emission (GATE) simulation tool. The results showed that the full width at half maximum (FWHM) of the center source were 6.25 mm and 7.18 mm for single-pinhole and multi-pinhole collimators, respectively. Moreover, limited angle reconstruction resulted in a higher efficiency of the imaging system because it overcame the limitation of the gantry geometry. Limited-angle reconstruction was optimized at an angle coverage of 120° with an angle interval of 6°, then reconstructed image was shown a 12.18 mm FWHM. This suggests that the designed system needs only one-third the number of projections to acquire a reconstructed image with a slight degradation in image quality. This also suggests that our proposed multi-pinhole collimator is suitable for applications requiring a small-footprint, a fast-scan-time, and organ-specificity.